Usually this is done with a reed contact/switch in a hollow tube (stainless with closed bottom) and a round float with hole in the center around this with a magnet in it when the magnet drops far enough it will activate the reed contact. your pump has to stop. for this kind of application there would be two stops a bottom one to prevent the float from falling of the tube a top one to limit the floats top position so it just activates the reed contact (and not allows it to go past it ) Hope this helps Peter ----- Original Message ----- From: "John Waters" To: Sent: Tuesday, June 08, 2004 11:35 PM Subject: [EE]: water level detection, how? > Hi All, > > I have a tank with a submersible pump inside, I want to stop the pump from > running dry when the water level is too low, what sort of sensor could I > use? I'm thinking of using a float with a magnet attached, the magnetic > field will trigger a relay to turn off the power, does anyone get experience > in building this kind of thing and would like to share the experience with > me? > > Thanks in advance! > > John > > _________________________________________________________________ > Tired of spam? Get advanced junk mail protection with MSN Premium > http://join.msn.com/?pgmarket=en-ca&page=byoa/prem&xAPID=1994&DI=1034&SU=http://hotmail.com/enca&HL=Market_MSNIS_Taglines > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu